The present invention relates to the field of antennas, and more particularly, to an antenna employing an electromagnetic reflector and a transverse electromagnetic feed mounted on an electrically conductive strut through which electromagnetic energy is carried between the strut and the reflector.
During the past several years there has been growing interest in developing ultra wide band (a bandwidth extending several octaves) radio frequency systems. A key element in an ultra wide band radio frequency system is the antenna which provides the transmission of electromagnetic energy and/or detection of return signals. Planar wide band antennas and ridged horn antennas are two type of antennas which have been used in wide band radio frequency systems.
Planar wide band antennas may be either of the spiral or sinuous type. In cases where the spiral arms are fed in antiphase to the center of the antenna, the spiral arm radiates energy in bidirectional beams perpendicular to the plane of the spiral. In many applications, bidirectional beams are not desired due to the generation of back lobe radiation. Therefore, spiral type planar wide band antennas typically employ back cavities so that they only generate unidirectional radiation. The construction of a spiral type planar antennas generally involves printing spirally shaped metal strips on one side of the substrate layer of the supporting substrate which is then inserted inside a metal cavity. This type of antenna is generally not suitable for high power applications because of the limitations of the dielectric breakdown properties of the supporting materials. Moreover, since a spiral type of planar antenna does not use a parabolic reflector, this type of antenna has a very low gain.
A sinuous type of planar antenna is very similar to a spiral type of planar antenna, except that the spiral strips are replaced by a sinuous pattern of metal strips formed on the sides of the substrate. The major drawbacks for this type of antenna are low power handling capabilities and low antenna gain.
The ridged horn antenna is another type of broadband antenna that is often used in communications applications. A ridged horn antenna is generally composed of two flanges which carry electromagnetic energy from the signal source to the illumination area of the ridge horn antenna. An impedance transformer is normally inserted between the two flanges to match the input impedance of the antenna to the source. For low frequencies (generally less than 1 GHz), this type of antenna is very lengthy, and difficult to construct. The antenna gain of the ridged horn antenna typically is higher than that of the spiral and sinuous types of planar antennas. However, the gain of the ridged horn antenna is generally less than most directional narrow beam antennas, making the ridged horn antenna unsuitable for applications which require high gain.
A reflector is often used to achieve a required level of gain for a highly directional antenna. A reflector antenna generally includes a reflector dish and a feed horn which may exist in several configurations. Two well known configurations of a feed horn antenna are the rectangular horn and cylindrical horn. In such configurations, the feed horn is a radiator mounted at the focal point of a reflector. Electromagnetic energy radiates from the feed horn to the metallic surface of the reflector dish from which it is directed into free-space. Mechanical struts support the feed horn at the focal point of the reflector, but have no electromagnetic function.